Earth-shaking 'wobble' may have killed dinosaurs

A mosaic of Mercury created from images taken by Mariner 10 during its approach on March 29, 1974

By Thom Patterson
CNN.com

(CNN) -- The extinction of the dinosaurs 65 million years ago may have been caused by a kind of astronomical "wobble" in Earth's and Mercury's solar orbits, according to a new theory by a group of California scientists.

Scientists have long speculated that a giant celestial body slammed into ancient Earth near what is now Mexico's Yucatan Peninsula.

The impact, known by scientists as K-T, threw so much dust into the atmosphere that the resulting darkness killed plants that many dinosaurs relied on for food, according to the widely accepted theory. The dinosaurs essentially starved to death.

But it's unclear if the object that hit the Earth was a comet or an asteroid.

Using computer models, University of California at Los Angeles professors Bruce Runnegar, Michael Ghil and researcher Ferenc Varadi tracked planetary orbits as far back as 250 million years ago.

That wobble, in turn, may have caused the planet Mercury's orbit to wobble. Gravitational effects of the two celestial wobbles might have forced a large asteroid to break away from the asteroid belt and smash into Earth, according to research by Varadi and his colleagues.

There are thought to be hundreds of thousands of asteroids in our system ranging in size from small pieces to as large as entire mountains. Most of them are floating in the main asteroid belt, an elliptical plane located between Mars and Jupiter.

Mark Bailey, director of the Armagh Observatory in Northern Ireland, said he is also studying what might have hit the Earth and driven the dinosaurs to extinction.

"I'm skeptical," Bailey said of the theory. "It seems to me that this is a very long chain of assumptions." But Bailey said he could not rule out the theory altogether.

"It is true that it is the result of assumptions," Varadi said. "But something definitely happened to the orbit of Mercury, and it is very difficult to ignore the coincidence of that event occurring at the same time as the K-T impact."

Bailey said it was much more likely a comet -- not an asteroid -- that smashed into the Earth 65 million years ago.

Unlike asteroids, comets are huge chunks of debris, constantly hurtling through space in what usually are highly eccentric orbits.

But Varadi, a 20-year veteran researcher who hails from Hungary, said that if he had to guess whether the object that hit the Earth was a comet or an asteroid, he would choose the asteroid theory.

"This will probably result in a new direction of research," said Varadi, 42, adding that the discovery will likely attract the interest of other scientists who will work toward confirming the new theory.